Our implementation of the two-step GFPCA approach of [1]} is based
on their accompanying package gfpca [2]}.
Additionally we made several adjustments to their codebase to improve overall efficiency:
First, while functions lmer() and glmer() from the
lme4 package default to the optimization
routine implemented in function bobyqa
[3]},
we make use of the more efficient optimizer NLOPT_LN_BOBYQA
from the NLopt library [4]} as described in [5]}.
